Simply because:

We see REDD as a Driver of the Continent Grab
In Africa, REDD+, carbon credits, agrofuels and export crops, are driving huge land grabs. Furthermore, since REDD+ now includes plantations and agriculture, already existing plantations, agrofuels and export crops could soon become carbon offset projects as well. Experts are warning that three-quarters of Africa’s population and two-thirds of its land are at risk and that REDD+ may create “generations of landless people.” In Africa, REDD+ is emerging as a new form of colonialism, economic subjugation and a driver of land grabs so massive that they may constitute a continent grab.

REDD is a New Form of Colonialism?
It is worth noting that there are several nuances that distinguish this new form of colonialism from classic colonialism. For example, foreign investors are not all from Europe or the United States, but also hail from the Global South, in particular, from Brazil. In addition, foreign investors are not acting on their own and political and economic elites are facilitating the expropriation of peasant lands and indirectly engendering hundreds of land conflicts. Furthermore, while land is till the issue supreme, the principal export commodity of this new form of colonialism is novel: air.

Also...

According Timberwatch, “The danger [REDD] presents to Africa is enormous. If REDD-style schemes are allowed to be imposed on African forestland, fields and grasslands, it could mean the economic subjugation of the entire continent. Without absolute guarantees that human and sovereign rights of African peoples will be fully respected and protected, which is unlikely to be the case, REDD and CDM schemes will probably be no more than a form of re-colonisation, and the final drive to commodify the remaining spaces of Africa left in indigenous hands after the first round of formal colonialism.